Flip-chip mounting is one of the methods of mounting a semiconductor element on a circuit board. In the flip-chip mounting, the circuit board and the semiconductor element are electrically and mechanically connected to each other by reflowing and connecting solder bumps formed on the surfaces of the circuit board and semiconductor element.
As the solder bumps are miniaturized, the distances between the adjacent solder bumps get shorter. This can cause an electrical short circuit between the bumps which are melted by reflow. Moreover, as the solder bumps are reduced in diameter with the miniaturization, the density of current flowing through the solder bumps increases. This can notably cause electromigration in which the solder material flows along the current.
To avoid such problems, instead of using the connection method using solder bumps, there is proposed a method in which the electrodes, such as copper bumps, are bonded by performing thermocompression bonding on the electrodes, thereby causing solid phase diffusion of the metal materials in the electrodes. This bonding method is also referred to as solid-phase diffusion bonding.
In the solid-phase diffusion bonding, unlike the connecting method using solder bumps, it is unnecessary to melt electrodes by reflow. Therefore, even when the distances between the adjacent electrodes are reduced, the electrodes cannot be electrically short-circuited. The solid-phase diffusion bonding is therefore advantageous to miniaturization of electronic devices.
However, in the process of the solid-phase diffusion bonding, to promote diffusion of atoms between the electrodes, high temperature and high pressure are applied to semiconductor elements. This can damage the semiconductor elements.
The technologies related to the following disclosure are disclosed in Japanese Patent Laid-open Publications No. 04-309474 and No. 05-131279.